In prior art, the CNC (Computerized Numerical Control) spinning forming method is widely used to form the truck wheel discs at home and abroad, The method spins an equal-thickness blank into an equal-strength section with gradually reduced thickness. The technological process of spinning forming method is as shown in FIG. 1:
a. Baiting a circular blank and punching a positioning hole for spinning.
b. Spinning the blank into a wheel disc by the CNC spinning forming method on a tapered circular cylinder exploratory so as to meet the requirements of forming an equal-strength section which gradually becomes thinner.
c. Processing the excircle and the end surface of the spinning formed wheel disc in a dedicated vertical lathe in order to meet the requirement on the tolerance of the outer diameter and the requirement that the height of the wheel disc should be uniform. (This step aims at to attain the dimensional precision requirement of products, which the spin-forming technology can not achieve).
d. Punching a center hole and screw holes.
e. Punching hand holes (air holes) and then extruding the hand holes (air holes).
f. Reaming the spherical surfaces of the screw holes (or extruding the spherical surfaces of the screw holes).
g. Turning the center hole (or extruding the center hole).
h. Reshaping the flat surface and unifying the geometrical shape (for avoiding the out-of-roundness of the single air hole caused by irregular deformation during punching).
As shown in FIG. 2 and FIG. 3, the existing spinning technology performs spinning on a work piece (circular blank) R with a spinning wheel P. The larger the spinning angle (α1+α2) of the spinning technology, the larger the spinning gripping angle (α3+α4) of the spinning wheel. Furthermore, the smaller the gripping angle, the stronger the extrusion force, therefore the extrusion force of the existing spinning technology is smaller. In addition, because the spinning explorator Q is cylindrical, and the forming method on the spinning explorator Q is an open type forming way without deformation size limitations, the well extrusion effect can not be achieved. Besides, fewer limitations on the spinning forming method and nonuniformity of the materials will result in instability of the spinning wheel P along with the changes in resistance during the movements of spinning wheel P, which cause small deformation on hard portion of the material whereas large deformation on soft portion, so micro-uneven conditions in the axial direction and the circumferential direction of the wheel disc will be brought about, and consequently the unbalance of the wheel disc. On the other hand, turning of the excircle will generate turning eccentricity, which can also further increase the unbalance of the wheel disc, as a result the precision of the excircle of the formed product can not meet the matching dimensional precision, and the spinning ring is retained on the formed product, which makes excircle processing in the vertical lathe indispensable. Furthermore, because of the unevenness of the height of formed product due to the material nonuniformity, turning of the end surface is necessary. Thus it can be seen, the only way to improve the spinning efficiency is to increase the number of the vertical lathes and the number of staffs. However, the production cost is also increased.